A polymeric PTC device is a device that interrupts current flow by utilizing the positive temperature coefficient (PTC) of a conductive polymer, which decreases conductivity through thermal expansion. Polymeric PTC devices in the prior art had a construction wherein a conductive polymer is sandwiched between two electrodes; when current required to thermally expand the conductive polymer flows between the two electrodes, or when the PTC thermistor is placed under a prescribed temperature environment, it functions to radically reduce the current flow between the electrodes.
There are also constructions, based on the polymeric PTC thermistor with the above construction, where a heat source that generates heat in response to some influence is added in a heat-transferable fashion. This polymeric PTC thermistor can radically reduce the current flow between the electrodes by activating the heat source at a desired timing, and heating the conductive polymer to expand it thermally.
As prior art relative to the above, for example, in Japanese Patent Publication No. S56-38617, there is described a constant voltage device that controls voltage by utilizing heat radiation from a PTC ceramic layer 1B provided between input electrodes 2, 3 and the output electrode 6.
In the latter polymeric PTC thermistor that can interrupt current flow at a desired timing, a heat source and apparatus to activate the heat source are required in addition to the former polymeric PTC thermistor, and there was a drawback because the construction became complex and the manufacturing cost became higher. Another problem was that the module became large because there were many components.
This invention was made in view of the above circumstances and is intended to provide a thermistor that has a simple and compact construction and can be supplied inexpensively.